Processes for forming thermoplastic resin films can be classified into two large categories solution film forming process and melt film forming process The solution film forming process is a process in which a dope of thermoplastic resin in a solvent is cast from a die upon substrate(s), for example, cooling drum(s) into a film, while the melt film forming process is a process in which a thermoplastic resin is molten in an extruder and the molten resin is extruded from a die upon substrate(s), for example, cooling drum(s) into a film Traditionally, the thermoplastic resin films formed by these processes are stretched in the longitudinal direction (lengthwise direction) and in the transverse direction (widthwise direction) so that they develop in-plane retardation (Re) and retardation in the thickness direction (Rth), and such stretched films have been used as a retardation film for liquid crystal display devices to achieve a wider viewing angle in such displays (e.g. National Publication of Internal Patent Application No 6-501040 and Japanese Patent Application Laid-Open No 2001-42130)
In recent years, however, retardations (Re, Rth) of retardation films requested by manufacturers of liquid crystal display devices have varied from manufacturer to manufacturer, and besides, there have been increasing demands for films with retardations close to 0 nm This is probably because use of a film with retardations close to 0 nm, in other words, use of a film showing a small optical anisotropy makes it easier for manufacturers of liquid crystal display devices to work out an optical design in film processing